Tactical rifles and other types of firearms commonly are equipped with a gas system configured to capture energy, in the form of high-pressure gas, generated by the discharge of the firearm. The energy is used to activate and cycle a mechanism, or action, that automatically reloads the firearm. Gas-actuated firearms typically include a gas block mounted on a barrel of the firearm. The gas block has a gas port that aligns with a corresponding gas port that is formed in the barrel. The barrel gas port extends between the exterior of the barrel, and an internal bore within the barrel.
When a cartridge, i.e., a round of ammunition, is discharged within a firearm, a projectile of the cartridge is propelled through the bore by high-pressure gas generated by the ignition of propellant within the cartridge. When the propellant gas reaches the barrel gas port, a portion of the propellant gas enters that port. The propellant gas subsequently enters the gas block by way of the gas port formed in the gas block. The propellant gas flows from the gas block gas port into an internal passage formed within the gas block. The pressurized propellant gas then travels to the action of the firearm by way of a gas tube that forms a gas path between the gas block and the action. The action is energized by the propellant gas, and is configured to eject from the firearm the now-empty case of the fired cartridge, strip an unfired cartridge from a magazine of the firearm, and load the unfired cartridge into a chamber of the barrel.
The action is designed to operate when the propellant gas is within particular a range of pressures and flow rates. Under varying circumstances, the pressure of the propellant gas within the bore of the barrel can vary, which in turn can affect the pressure and flow rate of the propellant gas reaching the action. For example, the use of a sound suppressor on a firearm typically raises the gas pressure within the bore. This is due to the increase in back pressure within the bore resulting from the additional flow restriction introduced by the suppressor. The pressure in the bore also can vary with the type of cartridge being fired. Increases in the pressure and flow rate of the propellant gas reaching the action may cause these operating parameters to exceed the levels at which the action is designed to operate, increasing the potential for premature wear and damage to the action, and jamming of the firearm.
Various means have been employed in an attempt to regulate the flow of propellant gas to the action of a gas-operated firearm. For example, the flow of propellant gas has been regulated using gas blocks configured to be moved into different positions on the barrel, so as to align the gas port of the gas block with differently-sized gas ports formed in the barrel. This technique can be problematic, however, because the gas block often becomes stuck to the barrel due to the accumulation of propellant gas residue between the gas block and the barrel.
Other techniques rely on the use of removable sleeves positioned within the gas block, or at other locations in the gas path. The sleeves provide different degrees of flow restriction; and a particular sleeve can be installed when it is necessary or otherwise desired to alter the flow restriction. This technique, however, usually requires cumbersome component disassembly involving the use of external tooling, and also requires that the user have on hand an appropriate sleeve to achieve the desired degree of restriction. Techniques that require disassembly and reassembly and the use of external tooling can be particularly disadvantageous in military and law enforcement applications where flow restriction may need to be adjusted under exigent circumstances, at night or under other low-visibility conditions.
Other flow-restriction techniques employ a flow restriction device that is located within the action, and that provides a different degree of restriction depending on the rotational position of the device. These devices may require external tooling to set the desired level of flow restriction; may remain directly in the gas path at all times, thus introducing an additional flow restriction and pressure drop when not desired; and may not provide the user with positive tactile feedback that a particular degree of flow restriction has been set.